Natural gas which comprises a mixture of gases including methane, ethane and propane is a by-product of oil recovery from subterranean reservoirs. The presence of these gases at the well site or possibly as by-products from petroleum refining operations constitutes an undesirable element inasmuch as a necessity is present for recovery of these gases in an economical and safe manner. Therefore, there is a need at these sites to provide some process for transporting this material away from the well site or refinery site in such a manner so that it is possible to utilize these gases in a commercially attractive manner. One method which has been employed in recovering an oversupply of a low carbon content gas such as methane is to convert the methane into methyl alcohol. However, the conversion of methane into methyl alcohol possesses some inherent disadvantages inasmuch as the process for the conversion requires several steps. After obtaining the alcohol, it is then necessary to convert this alcohol into other products.
Another method of treating the unwanted low molecular weight gases is to convert said gases into a halide. For example, it is relatively easy and inexpensive to convert methane into methyl chloride using existing technology which involves conversion processes. This conversion step to the organic halide can be readily accomplished at a well site or refinery site. However, the resulting organic halide must then be converted into usable, easily transportable products for further use in the chemical industry. Examples of usable products which find a wide variety of use in the chemical field will include aromatic compounds such as benzene, toluene, the isomeric xylenes, ethylbenzene, etc. as well as straight or branched chain hydrocarbons containing 4 or more carbon atoms in the chain such as butane, butene, pentane, pentene, hexane, hexene, as well as the isomeric molecules, etc.
As will hereinafter be shown in greater detail, we have now discovered that methane may be treated with a halide agent to form a methyl halide following which the methyl halide may be converted into usable products by contacting said halides with a particular type of crystalline silica material. Prior U.S. patents have disclosed various methods for treating alkyl halides or other compounds to form desirable products. For example, U.S. Pat. No. 3,894,107 discloses a method for the conversion of alcohols, mercaptans, sulfides, halides, and/or amines to form desirable compounds. However, the catalyst which is utilized to effect this conversion comprises a particular type of a crystalline aluminosilicate catalyst which, as will hereinafter be set forth in greater detail, differs in many respects from the catalyst which is used to effect the process of the present invention. U.S. Pat. Nos. 3,894,105 and 4,524,234 teach a method for the conversion of compounds such as methyl chloride. However, these patents do not suggest such conversion is accomplished in the presence of the particular silicalite catalyst which is used in the present invention. U.S. Pat. No. 2,488,083 is directed to a process for the manufacture of liquid hydrocarbons by the condensation of alkyl halides in a dehydrohalogeno-condensation reaction. However, the inventive concept of this patent resides in the use of a diluent such as C.sub.2 to C.sub.4 hydrocarbons produced during the reaction in the reaction zone. The presence of such diluents enhances the liquid hydrocarbon content of the product which is a fact conformed by both the examples and the specification of this patent. U.S. Pat. No. 4,579,996 teaches the conversion of methyl chloride over a catalyst comprising a clay which contains either hydrogen ions and/or metal cations which have been introduced into the catalyst either by exchange and/or by deposition. Table 1 of this patent indicates that the methyl chloride is converted primarily to hydrocarbons containing from 1 to 5 carbon atoms.
U.S. Pat. No. 4,384,159 discloses a process for treating saturated hydrochlorocarbons containing from 1 to 6 carbon atoms with a silicalite catalyst in a dehydrochlorination process to form olefinic compounds. The dehydrochlorination process which is effected in this patent relates to the elimination of the constituents of hydrogen chloride from adjacent carbon atoms of an alkyl halide to afford a carbon-carbon double or triple bond. This is an art-recognized reaction which does not provide for an increase in the number of carbon atoms in the products compared with the reactants. The examples present in this reference describe the production of olefinic products such as vinylchloride and ethylene from ethylene dichloride, ethylene from ethyl chloride, and 1,2-dichloroethylene from 1,1,2-trichloroethane.
As will hereinafter be set forth in greater detail, in contrast to the sample dehydrochlorination process which is described in U.S. Pat. No. 4,384,159 and as exemplified by reactants containing 2 carbon atoms, we have unexpectedly discovered that by forming a methyl halide from methane and contacting the resultant methyl halide with the silicalite catalyst of the present invention will result in the formation of products which are distinctly different from those described by this patent. Instead of resulting in the formation of hydrocarbon products which possess a carbon atom number corresponding to the feedstock, we will form paraffins, olefins, and aromatic products containing from 2 to 8 or more carbon atoms in the product, the production being produced from a feedstock containing a single carbon atom.
The formation of such products by utilizing the process of this invention may involve several reaction mechanisms including condensation reactions which combine small molecules into larger ones; oligomerization which is the combination of small molecules into larger molecules without the loss of a simple molecule; cyclization, which is the production of a compound containing a ring derived from an acyclic molecule having the same number of carbon atoms; aromatization, which is the conversion of small hydrocarbons into aromatic compounds and may include such steps as oligomerization, cyclization, and dehydrocyclization (cyclization accompanied by the loss of hydrogen), or alkylation, in which an alkyl side chain is attached to an aromatic ring.